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This invention relates to fuel systems for internal combustion engines and more particularly to stratified charge and torch ignition engines.
Direct injection, combined with stratified charge and torch ignition is an effective means for simultaneously reducing emissions and fuel consumption in spark ignition engines. In most prior art concepts, air-fuel mixture stratification is obtained by physically dividing the combustion chamber into a main chamber and an ignition chamber. The two distinct chambers are fluidically connected by means of one or more torch nozzles. A lean mixture, generally prepared outside the cylinder, is supplied to the main chamber. A small amount of fuel is injected directly into the ignition chamber, thus forming a rich mixture therein. This rich, easily ignitable mixture is then ignited, in the ignition chamber, and the resulting flame is ejected through the torch nozzles, thereby igniting the lean mixture from the main combustion chamber.
The most recent designs achieve mixture stratification utilizing only direct fuel injection and controlled fluid movement inside the cylinder. Inducing and controlling the fluid motion is sometimes accomplished entirely inside the cylinder, using special piston and combustion chamber shapes. Alternatively, the motion is initiated externally, by means of specifically profiled induction profiles and then it is maintained and controlled in the cylinder. A separate spark plug is necessary to initiate combustion.
Some disadvantages of the prior art designs are:
Complicated combustion chamber and intake duct design;
The engine must be specifically designed to operate as a stratified charge engine, requiring special piston and cylinder head shapes;
Most designs use two separate fuel systems to achieve charge stratification;
Most designs use a separate spark plug to ignite the fuel, thereby making the implementation of this method to the modern, multi-valve engines, a challenging task.
The device of the invention overcomes the aforementioned disadvantages of the prior art by utilizing a single injection and ignition device to supply the fuel, form the stratified charge and ignite the fuel. The injection device effectively divides a predetermined fuel dose into a main dose and a substantially lesser pilot dose. The main and the pilot dose are injected during the compression stroke of the engine. The variable cylinder pressure during the compression stroke is used as a means to control fuel flow rate and fuel jet penetration into the combustion chamber.
The pressure rise inside the engine during the compression stroke co-operates with the device geometry to ensure the formation and optimum spatial placement of a rich mixture kernel, and to control the formation and spatial distribution of a lean mixture field.
At a predetermined time, an integrated ignition source provides an electric spark, which ignites the rich mixture. The subsequent combustion flames propagate through the lean mixture field, thereby promoting the torch ignition of the fuel thereof.
Objects and advantages.
Accordingly, several objects and advantages of the invention are:
The compact injection and ignition device of the invention can be easily installed on modern multi-valve engines;
Instead of relying on combustion chamber geometry to form and control charge stratification, the device of the invention utilizes its own geometry, in co-operation with the variable cylinder pressure instead. Therefore the injection and ignition device of the invention can be installed on a variety of existing engines, requiring only small constructive changes.
The injection and ignition device of the invention can be used for fueling an engine with a traditional liquid fuel, such as gasoline, or with a gaseous fuel, whereby the device can be used to convert a Diesel engine to operation on a gaseous fuel, with only minimal constructive modifications of the pistons or cylinder head.
The injection and ignition device of the invention permits the modified spark ignition engine to run on an overall leaner mixture than a traditional, homogenous charge, spark ignition engine, with superior efficiency, approaching the Diesel cycle.